The methods of optogenetics enable light-induced, area-confined stimulation or inhibition of genetically targeted neurons, thereby bypassing key disadvantages of electrical approaches. As a result, optogenetics is now widely viewed as an essential tool in neuroscience research. The adoption of these methods by the community is rapidly increasing, in spite of the required use of an expensive, inconvenient collection of fiber optic cabling, ferrules/fixtures and external light sources to perform the experiments. These systems restrict natural behaviors in animals and frustrates entire classes of experiments such as those that involve social interactions and complex three dimensional environments. The proposed program focuses on the development of ultraminiaturized, fully implantable wireless systems capable of delivering light to targeted regions the brain, the spinal cord and the peripheral nerves for optogenetics research. High volume, low cost manufacturing techniques that align with those in widespread use in the flexible printed circuit board industry will allow these lightweight components to be produced in mass quantities and price points that will allow broad adoption, even by resource constrained labs. The versatile capabilities of these systems and their ease of use will significantly increase the access of optogenetics techniques to broad segments of the neuroscience community. Initial proof-of-concept devices offer unique advantages over any other research or commercial alternative, including mm-scale dimensions (10x smaller), mg weights (100x lighter), sub-mm thicknesses (10x thinner), mechanically flexible architectures, proven capabilities in chronically stable operation, broad compatibility with single or multiple animals in simple or complex environments, and straightforward, robust wireless interfaces. The specific aims of the proposed work are to develop (1) designs that are compatible with low cost, high volume manufacturing, (2) advanced versions with capabilities for multi-wavelength, multichannel operation with expanded wireless coverage and applicability to the brain, spinal cord and peripheral nerves and (3) new systems that perform not only light delivery but also photodetection, for operation in wireless photometry and closed-feedback optogenetic stimulation/inhibition.